Thanks to the release of version 6.0 yesterday, Switch owners now have the ability to play their downloaded games and content on a second console. The functionality works by having users designate “primary” and “non-primary” consoles through their Nintendo Account.
If a Switch owner is without their own console but has access to someone else’s, it’s possible to log into their Nintendo Account on this non-primary console and play all of their digital game content on it. The catch is that users will have to maintain an internet connection while playing their owned content on any non-primary console. If the user loses their internet connection, then the game will pause “after a certain amount of time.” The player can resume where their game was paused once a connection is reestablished.
Source: IGN.com Switch Owners Can Now Play Their Games on More Than One Console